Silver alloy for reflective film of optical recording medium

ABSTRACT

The present invention provides a silver alloy for use in a reflection coating for an optical recording medium, comprising silver as a main component and indium and/or tin as an additive element. It is preferable when the concentration of the additive elements falls within 0.1-25 wt %, and reflectivity can be inhibited from deteriorating especially when the concentration falls within a range of 0.1-5.0 wt %. When the thermal conductivity of the reflective layer is taken into account, the concentration of the additive elements may be further limited to 0.1-0.5 wt % to provide a reflective layer of higher thermal conductivity.

TECHNICAL FIELD

The present invention relates to a silver alloy suitable as aconstituent material for a reflection coating for an optical recordingmedium, especially to a silver alloy for a reflection coating, which iscapable of inhibiting decrease in reflectivity during a long-termservice.

BACKGROUND ART

Optical recording media such as CD-ROM, DVD-ROM or the like normallycomprise a substrate on which a recording layer, a reflection coatinglayer and a protective layer (i.e. overcoat) are provided. As areflection coating layer, an aluminum alloy has been used conventionallyfrom the viewpoint of cost and reflectivity. However, application ofmaterials having higher reflectivity has been demanded as the mainstreamof optical recording media shifts to recordable or rewritable ones(CD-R/RW, DVD-R/RW/RAM). This is attributable to a fact that organic dyematerials have been widely used as a constituent material for arecording layer in recordable or rewritable media, and organic dyematerials allow extinction of a light beam to become great, so that theextinction should be compensated by improved reflectivity of areflective layer.

In terms of reflectivity, it is silver that has been applied as amaterial for a reflective layer in an optical recording medium. Silveris a suitable material in view of higher reflectivity and moderate pricecompared to gold, which also has higher reflectivity. However, silverhas a disadvantage that it is poor in oxidation resistance and sulfurresistance, hence it readily corrodes due to oxydation or sulfurationand will turn black to deteriorate the reflectivity.

In order to address a problem of deterioration in reflectivityassociated with the use of an optical recording medium, efforts havebeen conventionally made to develop optical recording media, to whichsilver alloy is applied as a reflective layer to increase corrosionresistance while reflectivity is secured. Many of these media haveadopted silver as a main component, to which one, two or more differentadditive elements should be added. Specifically, some cases have beendisclosed where 5-10 at % ruthenium and 0.1-10 at % aluminum are addedto silver, or 0.5-4.9 at % palladium is added. It is further disclosedthat these silver alloys have good corrosion resistance and can maintainreflectivity under an operating environment, thereby being suitable as areflective layer (See Japanese Patent Publication Laid-Open Nos. Hei11-134715 and 2000-109943 for details of these prior art).

Certain degree of improvement has been recognized in terms of corrosionresistance in connection with the above-discussed silver alloys.However, these silver alloys are not always corrosion-free under someoperating environments. Moreover, deterioration in reflectivity has notbeen addressed completely, so that such materials capable of maintainingreflectivity in a higher dimension are demanded.

In the field of optical recorders, red semiconductor laser (wavelengthof 650 nm) is currently applied as a light source for recording, howeverpractical use of blue laser (wavelength of 405 nm) has been in sightrecently. Application of blue laser can insure a five- or six-foldstorage capacity compared to the present optical recorders, so that itis considered blue laser-applied optical recorders will becomemainstream in the next-generation ones. In this regard, the presentinventors have confirmed the reflectivity of a reflective layer willfluctuate in accordance with the wavelength of laser to be irradiated,and especially have confirmed irradiation of laser having ashort-wavelength will cause deterioration in reflectivity irrespectiveof presence or absence of corrosion and the deterioration inreflectivity due to corrosion will be prominent more frequently than ina case of irradiation of laser having a long-wavelength. Thus, in orderto manufacture recording media capable of addressing the futuredevelopment of light sources for recording, it is desired a developmentof materials having a higher reflectivity with respect to irradiation oflaser of short-wavelength band and capable of maintain a furtherpractical scope of use.

The present invention has been made with the above matters as abackground, and it relates to a silver alloy composing a reflectivelayer in an optical recording medium. It is an objective of theinvention to provide a material for a reflective layer, capable ofserving with the reflectivity kept not deteriorated due to a long-termuse. Furthermore, the present invention provides a material having ahigher reflectivity with respect to laser beams of short-wavelength.

DISCLOSURE OF THE INVENTION

In order to solve the above problem, the present inventors determined toadopt silver as a main component as had been done in the earliertechnologies, and to discover suitable materials for a reflective layerfrom a different viewpoint from the earlier technologies. The reasonthat silver was selected as a main component is based on considerationof the advantages (higher reflectivity and lower cost) that silver hasas discussed above. An approach that the present inventors made in adifferent manner from conventional one was to address the improvement ofcorrosion resistance only, through adding additive elements as had beendone in the earlier technologies. Specifically, corrosion (oxidation) ofa reflective layer during use is inevitable in a practical sense.Therefore, the present inventors considered such a silver alloy suitableas a material for a reflective layer if it is not deteriorated inreflectivity when oxidized, while daring to permit oxidation during use.The present inventors came up with the present invention throughdiscovering a silver alloy causing no deterioration in reflectivity whenoxidized, to which added are/is indium and/or tin which arepreferentially oxidized over silver and do not affect the reflectivity.

The present invention relates to a silver alloy for use in a reflectioncoating for an optical recording medium, which comprises silver as amain component and indium and/or tin as an additive element.

Oxides to which indium and/or tin have/has been added as an additiveelement in the present invention are transparent, as it isunderstandable from the fact that they have been widely applied as atransparent electrode material thus far. In the silver-indium/tin alloyaccording to the present invention, the indium and/or tin are/isoxidized during use and the oxide(s) are/is transparent, thereby causingno damage to the reflectivity of the alloy. Further in the alloyaccording to the present invention, indium oxide and tin oxide aredispersed within the alloy, and an oxide layer composed of indium oxideand tin oxide are formed on the surface of the alloy. The oxide layerserves as a protective layer for the alloy against further oxidation,and inhibits the silver to be a base material against oxidation. Areflective layer to be formed with the alloy according to the presentinvention is capable of maintaining a reflectivity with the actiondescribed above.

Some DVD-ROMs among optical recording media have a dual structure, inwhich the combination of a recording layer and a reflective coatinglayer have been made dual from the viewpoint of insuring memorycapacity. When data are read out from the recording layer in the upperlayer of the DVD-ROMs having a dual structure, it is necessary to changethe focal point of an incident laser beam to allow the beam to transmitthrough the substrate and the recording layer and reflective layer inthe lower layer. Therefore, a transmission property as well asreflection property are demanded to a reflective layer in a DVD-ROM. Inthis respect, the alloy according to the present invention is excellentin transmittance, and applicable to the reflective layers in a DVD-ROMhaving a dual structure.

The content of the indium and tin as being additive elements in thepresent invention will be preferably both 0.1-25 wt % if maintenance ofreflectivity should be taken into consideration. The reason is that whenthe added amount is less than 0.1, it is not effective in terms ofmaintenance of reflectivity, and when the concentration of addedelements exceeds 25%, some environments and wavelengths of incidentlaser beams may substantially reduce the reflectivity, causing a majorpractical obstacle. Especially preferable concentration is 0.1-5.0 wt %.The reason is that, if fallen within the range, the reflectivity can bemaintained at higher levels regardless of the environment and wavelengthof a laser beam. It should be noted that these ranges of concentrationindicate for all the additive elements, and when both indium and tin arecontained, it is indicated that the total concentration of each elementis within these ranges.

The silver alloy according to the present invention is suitable as amaterial for use in a reflective layer for an optical recording medium,and it is enumerated a higher thermal conductivity as a preferableproperty if provided to a material for an reflective layer. The reasonis that lower thermal conductivity of a reflective layer willdeteriorate the sensitivity of a recording medium. Thus, the silveralloy according to the present invention, which imparts propertiespreferable in terms of both maintenance of reflectivity and higherthermal conductivity, will be further preferable if it is provided witha concentration of additive elements such as indium and tin 0.1-0.5 wt%. The reason is that, according to the present inventors, such an alloyhaving a concentration of additive elements exceeding 5 wt % has a lowerthermal conductivity, and the additive elements will show only afraction of the thermal conductivity of silver, which is a maincomponent of the alloy.

As described above, the silver alloy according to the present inventioncan be produced through a melting and casting method. Production throughthe melting and casting method has no specific difficulties, and thesilver alloy can be produced through a common method in which each rawmaterial should be checkweighed, melted and mixed for casting.

In the meantime, actual production of a reflective layer most oftenconducted will be a formation of thin films thorough a sputtering methodin which a target comprising a material for a reflective layer isemployed. As described above, in the silver alloy according to thepresent invention, the iridium and tin contained are preferentiallyoxidized, and oxide thus generated will act as a protective film toinsure inhibition of oxidization and sulfuration, which will happensubsequently. When a reflection coating is formed with the silver alloyaccording to the present invention, oxygen is mixed with argon gas,which is to be introduced to a sputtering apparatus used in a sputteringmethod, reactive sputtering is conducted to form the reflective layerwhile oxidizing the same, thereby forming a protective film at anearlier stage of a reflective layer formation.

Meanwhile, the reactive sputtering may undermine a production efficiencyof a reflective layer because it needs subtle adjustment to anintroduction of oxygen gas in order to regulate the degree of oxidationof a reflective layer. In this regard, the present inventors came upwith an idea that in the present alloy, a normal sputtering processwithout introduction of oxygen gas, which requires subtle regulation canform a protective film to a reflective layer by preliminarily oxidizingindium and tin as additive elements. That is to say, the presentinventors determined to oxide partially or entirely indium and/or tin asadditive elements with respect to the silver alloy according to thepresent invention in which silver is a main component. They discovered athin film produced with the internally oxidized alloy employed as atarget will be formed to have oxides of indium and tin uniformlydispersed compared with the one at the production stage of a thin film.

Production of the internally oxidized silver alloy can be effectedthrough: producing a silver alloy containing predetermined compositionsof indium and/or tin; and pressurizing and heating the silver alloy in ahigh-pressure oxygen atmosphere to allow the indium and tin in the alloyto be oxidized partially or entirely. As specific conditions foroxidation, it is preferable if the pressurization and heating areconducted in an atmosphere of oxygen tension 0.1-1 MPa at 700-800° C.for 60-80 hours.

The above-described silver alloy according to the present invention haspreferable properties as a reflective layer, and has been inhibited fromdeteriorating in reflectivity during use. Further, the silver alloyshows better reflectivity and maintenance thereof compared to theconventional materials for a reflective layer even under irradiation oflaser beams of short wavelength, as described later. As described above,a sputtering method is generally applied in producing a reflective layerfor an optical recording medium. Thus, the sputtering target comprisesof the silver alloy according to the present invention is contributiveto production of an optical recording medium provided with a reflectivelayer having preferable properties.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, examples of the present invention will be describedtogether with comparative examples.

EXAMPLE 1

In this example, a target as a silver alloy composed of Ag, In 1.2 wt %,and Sn 0.8 wt % was produced, and a thin film was formed throughsputtering with the use of this target. Thus formed thin film wassubjected to corrosion tests (acceleration tests) under variousenvironments for studying variations in reflectivity of post corrosiontests.

In producing a silver alloy, each metal was checkweighed to reach apredetermined concentration, and is molten and mixed in a high-frequencymelting furnace to prepare an alloy. Then, it was poured into a mold tosolidify for preparing an ingot, which was forged, rolled,.heat treated,and formed to produce a target.

In producing a thin film, a substrate (borosilicate glass) and a targetwere placed in a sputtering apparatus. After a vacuum was drawn in theapparatus to a level of 5.0×10⁻³ Pa, argon gas was introducedintroducedto a level of 5.00×10⁻¹ Pa. A film was formed under sputteringconditions with 1 kW of direct-current and time period of 1 minute tomake the film thickness 1000 Å. Distribution of the film thickness wasconfirmed within ±10%.

A corrosion test of a thin film was done with the thin film exposed toeach environment described below and with the reflectivity of a testedthin film measured while a wavelength was changed with the use of aspectrophotometer, and variation in reflectivity was inspected with thereflectivity of the silver of immediately after film formationstandardized.

(1) Heating at 250° C. for 2 Hours in the Atmosphere

The thin film was placed on a hot plate, and was heated in accordancewith the above prescribed temperature and duration of time. This testenvironment is for inspecting an oxidization resistance of the thinfilm.

(2) Soaking in Warm Water for 30 Minutes

The thin film was soaked in pure water of 60° C. This test environmentis for inspecting a moisture resistance of the thin film.

(3) Soaking in an Alkaline Solution

The thin film was soaked in a sodium hydroxide solution of 3%(temperature 30° C.) for 10 minutes. This test environment is forinspecting an alkaline resistance of the thin film.

COMPARATIVE EXAMPLE

As a comparison with the silver alloy according to the present examples,thin films were produced from three targets composed of silver alloys,specifically of Ag-1.0 wt % Au-1.0 wt % Cu, Ag-1.0 wt % Pd-1.0 wt % Cu,and Ag-1.0 wt % Nd-1.0 wt % Cu, and corrosion tests similar to theabove-described one were conducted to measure likewise variations inreflectivity.

The results of the corrosion tests in this example will be shown inTables 1 through 3. The reflectivity as shown in Tables are relativevalues when the reflectivity of the silver of immediately after filmformation is set to 100. Each measured value represents reflectivity inthe wavelengths of 400 nm, 560 nm, and 650 nm (corresponding to thewavelength of blue, yellow, and red laser, respectively.). TABLE 1Comparative Example Example 1 Ag—Au— Ag—Pd— Ag—Nd— Ag—In—Sn Cu Cu CuImmediately after 97 83 84 88 film formation 250° C.-2.0 h 94 88 92 93Soaking in warm 95 85 88 90 water Soaking in alkali 96 95 95 90 Averagevalue 96 88 90 90Wavelength of incident light: 650 nm

TABLE 2 Comparative Example Example 1 Ag—Au— Ag—Pd— Ag—Nd— Ag—In—Sn CuCu Cu Immediately after 95 82 80 80 film formation 250° C.-2.0 h 91 8288 90 Soaking in warm 94 84 84 82 water Soaking in alkali 94 93 93 82Average value 94 85 86 84Wavelength of incident light: 560 nm

TABLE 3 Comparative Example Example 1 Ag—Au— Ag—Pd— Ag—Nd— Ag—In—Sn CuCu Cu Immediately after 77 72 69 65 film formation 250° C.-2.0 h 70 5769 69 Soaking in warm 78 72 71 65 water Soaking in alkali 76 75 75 65Average value 75 69 71 66Wavelength of incident light: 400 nm

From the results, as the wavelength of incident light becomes shorter,the reflectivity will be deteriorated as a general trend (the same holdstrue for a thin film subjected no corrosion test immediately after filmformation). The thin film produced from the silver alloy according tothe present example shows higher values than any of the comparativeexamples in terms of reflectivity. Especially, the thin film accordingto the present example maintains the reflectivity of that of immediatelyafter film formation with respect to one tested about corrosion underany environment. However, the comparative examples show fluctuations inreflectivity depending on the environment for the corrosion test.Therefore, it is known that the thin film according to the presentinvention is a more preferable one as a reflective layer than thoseaccording to the conventional technologies.

EXAMPLE 2

In this example, a search was conducted in terms of the correlationbetween the concentration of additive elements and the reflectivity ofpost corrosion tests of the solver alloys, and the upper limits wereexamined. The silver alloys produced and employed in this example wereAg—Sn alloys, and silver alloys in which the tin concentration wasvaried in the ranges between 2-50 wt % were examined. The method forproducing the silver alloys in this example is the same as that inExample 1, however in terms of the corrosion test environment, a test inwhich the silver alloys were soaked in a 0.01% sodium sulfide solution(at the temperature of 25° C.) for 1 hour was conducted to examinesulfur resistance, in addition to the test environment of Example 1.Measurement of the reflectivity after the corrosion test was conductedin a similar manner to that in example 1. The results are shown inTables 4-6. TABLE 4 Corrosion test conditions Soaking in ImmediatelyHeating in the Soaking in Soaking in sulfide Sn after film atmospherewarm water alkali solution concentration formation (250° C. × 2 h) (60°C. × 0.5 h) (3% NaOH × 10 min.) (0.01% Na₂S × 1 h)  2 wt % 100 95 99 9998  3 wt % 99 97 99 99 98  4 wt % 98 97 99 98 94  5 wt % 97 97 98 98 8610 wt % 93 96 90 87 89 15 wt % 77 87 85 84 80 20 wt % 89 91 84 78 85 25wt % 84 86 84 85 84 30 wt % 84 84 62 81 83 40 wt % 78 76 72 78 77 50 wt% 70 74 73 55 72Wavelength of incident light: 650 nm

TABLE 5 Corrosion test conditions Soaking in sulfide Immediately Heatingin the Soaking in Soaking in solution Sn after film atmosphere warmwater alkali (0.01% concentration formation (250° C. × 2 h) (60° C. ×0.5 h) (3% NaOH × 10 min.) Na₂S × 1 h)  2 wt % 100 92 99 99 97  3 wt %99 96 99 98 96  4 wt % 97 96 99 97 92  5 wt % 96 96 98 97 94 10 wt % 9095 86 81 85 15 wt % 68 76 77 75 73 20 wt % 86 88 79 70 80 25 wt % 81 8380 82 81 30 wt % 81 80 59 79 81 40 wt % 74 71 68 74 73 50 wt % 67 67 6853 69Wavelength of incident light: 560 nm

TABLE 6 Corrosion test conditions Soaking in Immediately Heating in theSoaking in Soaking in sulfide Sn after film atmosphere warm water alkalisolution concentration formation (250° C. × 2 h) (60° C. × 0.5 h) (3%NaOH × 10 min.) (0.01% Na₂S × 1 h)  2 wt % 96 71 97 94 90  3 wt % 90 8495 89 87  4 wt % 83 81 93 87 75  5 wt % 83 76 88 82 80 10 wt % 75 84 7168 71 15 wt % 61 56 67 65 60 20 wt % 73 67 65 60 65 25 wt % 72 66 71 7373 30 wt % 72 61 52 70 72 40 wt % 66 55 61 66 64 50 wt % 63 46 55 51 63Wavelength of incident light: 400 nm

Considering the above results, it is understood from the trend in thepresent example that adding an additive element of 25 wt % or more willmake reflectivity at an initial stage (i.e. immediately after filmformation) lower depending on the wavelength of incident light, and whenan acceptance criterion as a reflective layer is set to 60 (thereflectivity of silver being set to 100), the silver alloys havingslight corrosion comes short of acceptance criterion in many cases.Therefore, it is estimated the upper limit of the content of theadditive element is 25 wt %. In order to keep the reflectivity as higherlevels (i.e. to show values of 80 or higher), the concentration of theadditive element should be preferably 5.0 wt % or lower.

EXAMPLE 3

For studying a lower limit of additive elements in this example,As—In—Sn alloys containing indium and tin in a total amount of 0.05-0.5wt % were produced, and then thin films were produced from the alloysfor measuring variations in reflectivity by way of corrosion tests. Aproduction method of the alloys, environments for corrosion tests andother conditions are the same as those in Example 2. The results areshown in Tables 7-9. TABLE 7 Corrosion test conditions Soaking inConcentration of Immediately Heating in Soaking in Soaking in sulfideadditive elements after the warm alkali solution (wt %) film atmospherewater (3% (0.01% In Sn Total formation (250° C. × 2 h) (60° C. × 0.5 h)NaOH × 10 min.) Na₂S × 1 h) 0.025 0.025 0.05 101 43 100 73 98 0.05 0.050.1 100 94 100 100 97 0.1 0.1 0.2 99 80 99 99 97 0.2 0.2 0.4 98 98 99 9996 0.25 0.25 0.5 99 98 98 98 96Wavelength of incident light: 650 nm

TABLE 8 Corrosion test conditions Soaking in Concentration ofImmediately Heating in Soaking in Soaking in sulfide additive elementsafter the warm alkali solution (wt %) film atmosphere water (3% (0.01%In Sn Total formation (250° C. × 2 h) (60° C. × 0.5 h) NaOH × 10 min.)Na₂S × 1 h) 0.025 0.025 0.05 101 36 100 72 97 0.05 0.05 0.1 101 92 100100 97 0.1 0.1 0.2 99 78 99 99 96 0.2 0.2 0.4 97 97 99 99 95 0.25 0.250.5 99 97 98 98 95Wavelength of incident light: 560 nm

TABLE 9 Corrosion test conditions Soaking in Concentration ofImmediately Heating in Soaking in Soaking in sulfide additive elementsafter the warm alkali solution (wt %) film atmosphere water (3% (0.01%In Sn Total formation (250° C. × 2 h) (60° C. × 0.5 h) NaOH × 10 min.)Na₂S × 1 h) 0.025 0.025 0.05 105 20 103 73 96 0.05 0.05 0.1 104 78 103103 95 0.1 0.1 0.2 97 62 98 97 94 0.2 0.2 0.4 93 88 95 95 91 0.25 0.250.5 89 83 93 92 89Wavelength of incident light: 400 nm

Considering the results, it is understood the silver alloys studied inExample 3 have good reflectivity immediately after film formation,however have large variations in reflectivity due to heating in theatmosphere. It is shown a correlation between the concentration ofadditive elements and reflectivity, and as the concentration of additiveelements becomes lower, the reflectivity after heating has a tendency todecrease. As in Example 2, when the acceptance criterion is set to 60,it is understood that the thin film having a concentration of additiveelements of less than 0.1 wt % (i.e. 0.05 wt %) can no longer maintainthe reflectivity of post-atmospheric oxidization. Therefore, it isconsidered appropriate to set the lower limit of the concentration ofadditive elements to 0.1 wt %.

EXAMPLE 4

For studying a correlation between the concentration of additiveelements and thermal conductivity in this example, As—In—Sn alloyscontaining indium and tin in a total amount of 0.05-0.5 wt % wereproduced, and then thin films were produced from the alloys forobtaining each thermal conductivity. The thin films were formed in thesame manner as those in Examples 1 and 2. Since it is difficult tomeasure the thermal conductivity of the thin films directly, specificresistance was first measured to allow thermal conductivity to beobtained through calculation in accordance with Wiedemann-Franz lawbased on the measured values. The results are shown in Table 10. Table10 specifically shows each thermal conductivity of three kinds of silveralloys as produced as Comparative Example of Example 1, which are ofAg-1.0 wt % Au-1.0 wt % Cu, Ag-1.0 wt % Pd-1.0 wt % Cu, and Ag-1.0 wt %Nd-1.0 wt % Cu, and the thermal conductivity of thin film of puresilver. TABLE 10 Thermal conductivity Concentration of Wm⁻¹K⁻¹ additiveelements Ag—In—Sn (wt %) (Present In Sn Total Example) Ag Ag—Au—CuAg—Pd—Cu Ag—Nd—Cu 0.025 0.025 0.05 237 240 106 45 63 0.05 0.05 0.1 2260.1 0.1 0.2 196 0.2 0.2 0.4 163 0.25 0.25 0.5 122 1.0 1.0 2.0 76

It is understood from Table 10 that the Ag—In—Sn alloy thin filmaccording to the present example exhibits thermal conductivity whichdecreases in proportion to increase in the concentration of additiveelements. When an acceptance line of thermal conductivity is set to be50% or higher of that of silver, it is considered appropriate to holdthe added amount of the additive elements below 0.5 wt % in view of thethermal conductivity. When the results of Example 3 are taken intoconsideration, it was confirmed preferable concentration of additiveelements in terms of two conditions, namely maintenance of reflectivityand high thermal conductivity, ranges 0.1 and 0.5 wt %. It was alsoconfirmed every silver alloy thin film according to Comparative Examplehas thermal conductivity of less than 50% of that of silver.

INDUSTRIAL APPLICABILITY

As described above and different from the conventional idea, the silveralloy according to the present invention inhibits reduction ofreflectivity during use through addition of elements, which generateoxide that causes no adverse effects on reflectivity when get oxidized.The present invention can produce a reflective layer less likely todecrease in reflectivity due to long-term use, thereby prolonging theduration of life of an optical recording medium. Further, the silveralloy according to the present invention exhibits better reflectivityand maintenance thereof than the conventional materials for a reflectivelayer even if subjected to irradiation of laser having ashort-wavelength Thus, the present silver alloy is applicable torecording media for optical recorders adopting a short-wavelength laseras a light source and expected to be a future mainstream.

1. A silver alloy for use in a reflection coating for an opticalrecording medium, comprising silver as a main component and indiumand/or tin as an additive element.
 2. A silver alloy for use in areflection coating for an optical recording medium according to claim 1,wherein said additive element has a concentration of 0.1-25 wt %.
 3. Asilver alloy for use in a reflection coating for an optical recordingmedium according to claim 1, wherein said additive element has aconcentration of 0.1-5.0 wt %.
 4. A silver alloy for use in a reflectioncoating for an optical recording medium according to claim 1, whereinsaid additive element has a concentration of 0.1-0.5 wt %.
 5. A silveralloy for use in a reflection coating for an optical recording mediumaccording to claim 1, wherein the indium and/or tin as an additiveelement has been internally oxidized partially or wholly.
 6. Asputtering target comprising the silver alloy according to claim 1.